1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and more particularly, to a bonding pad structure on a semiconductor element and a method of manufacturing the same.
2. Description of the Prior Art
FIG. 1 is a schematic cross sectional view showing a bonding pad portion of a conventional semiconductor device, and FIG. 2 is a plan view thereof. Referring now to FIGS. 1 and 2, description is made on a schematic structure of the bonding pad portion of the conventional semiconductor device. In FIG. 1, a field oxide film 2 is formed on the surface of the silicon substrate 1 into which a circuit element is incorporated. A silicon dioxide film (referred to as a PSG film hereinafter) 5 including phosphorus is then formed on the field xide film 2 as an insulating film. An aluminum (Al) film 6 is then formed on the PSG film 5 by evaporation or the like. An unnecessary portion of the aluminum film 6 is then etched away. An insulating protective film 7 is .then formed on the PSG film 5 to cover an end of the aluminum film 6. As a result, a semiconductor device having an opening 7a and comprising a bonding pad formed of the aluminum film 6 is obtained. The aluminum film 6 is used as a bonding pad, to which a lead (not shown) such as gold (Au) is electrically connected.
In the conventional semiconductor device, the PSG film is used as an insulating film, to lower the melting point of the film by including phosphorus, flatten the film and increase the coating ability of a stepped portion (not shown) or the like. It is desirable in a manufacturing process that the PSG film 5 is provided on the entire substrate. However, in the conventional semiconductor device, the aluminum film 6 is directly formed on the PSG film 5 without any material, so that impurities in the PSG film 5, particularly phosphorus, is liable to be diffused into the aluminum film 6. Therefore, there are some problems. For example, the inherent bonding ability of the aluminum film 6 is decreased, and a gold-aluminum alloy layer formed on an interface between the aluminum film and the lead is early deteriorated. In addition, water infiltrated between the aluminum film 6 and the PSG film 5 reacts on phosphorus to produce phosphoric acid, so that the produced phosphoric acid corrodes aluminum.
The prior art related to the present invention of the present application is disclosed in Japanese Patent Laying-Open Gazettes No. 9159/1985, 5660/1985 and No. 57646/1985. The Japanese Patent Laying-Open Gazette No. 9159/1985 discloses a technique to prevent aluminum and silicon (Si) from causing an eutectic reaction by providing a barrier layer between the aluminum film and the silicon substrate. The Japanese Patent Laying-Open Gazette No. 5660/1985 discloses a barrier layer sufficiently immune to the temperature cycle at a high temperature and having strong adhesion to a bonding material. In addition, the Japanese Patent Laying-Open Gazette No. 57646/1985 discloses a technique for avoiding the contact resistance of the aluminum film and the silicon substrate. However, the gazettes do not disclose any technique for preventing a reaction of phosphorus include in the PSG film and the aluminum.